Biomedical subjects

P A Turski

Publications and source records attributed to P A Turski.

At least 19 recordsLinked to original sources

PubMed2006

Subcortical reorganization in amyotrophic lateral sclerosis.

The cerebral cortex reorganizes in response to central or peripheral lesions. Although basal ganglia and cerebellum are key components of the network dedicated to movement control, their role in motor reorganization remains elusive. We therefore tested if slowly progressive neurodegenerative motor disease alters the subcortical functional anatomy of the basal ganglia-thalamo-cerebellar circuitry. Ten patients with amyotrophic lateral sclerosis (ALS) and ten healthy controls underwent functional magnetic resonance imaging (fMRI), while executing a simple finger flexion task. Cued by an acoustic trigger, they squeezed a handgrip force transducer with their right hand at 10% of their maximum voluntary contraction force. Movement frequency, amplitude, and force were controlled. Statistical parametric mapping of task-related BOLD-response revealed increased activation in ALS patients as compared to healthy controls. The main activation increases were found in the supplementary motor area, basal ganglia, brainstem, and cerebellum. These findings suggest that degeneration of cortical and spinal motor neurons in ALS leads to a recruitment of subcortical motor structures. These subcortical activation patterns strongly resemble functional activation in motor learning and might therefore represent adaptations of cortico-subcortical motor loops as a - albeit finally ineffective - mechanism to compensate for the ongoing loss of motor neurons in ALS.

Acoustic Stimulation↗

PubMed2001

Multiple tactile maps in the human cerebellum.

Functional imaging studies of the cerebellum have mostly investigated motor performance or have been limited to the anterior lobe and therefore the somatosensory representations in the human cerebellum have not been fully demonstrated. We used fMRI of the entire cerebellum during tactile stimulation of the hand and foot in six normal subjects. Our results demonstrate that the tactile projections to the cerebellum in humans are represented in both the anterior and posterior lobes. in agreement with previous functional imaging studies, our results show a large-scale, between-limb somatotopy comparable to that shown in early animal studies.

Adult↗

PubMed2001

Contrast-Enhanced magnetic resonance angiography of the carotid bifurcation using the time-resolved imaging of contrast kinetics (TRICKS) technique.

The time-resolved contrast-enhanced magnetic resonance (MR) angiographic technique TRICKS (time-resolved imaging of contrast kinetics) reconstructs a temporal series of three-dimensional (3D) images. The temporal resolution is increased by using a short TR (<8 ms) and TE (<2 ms), zero filling, partial echo sampling, view sharing, and temporally sampling k-space at variable rates. TRICKS allows reconstruction of multiple sequential 3D volumes following bolus injection of a gadolinium chelate (0.2 mmol/kg body weight up to 40 ml, injection rate -2 ml/s). The resulting temporally defined datasets are conceptually similar to a catheter-based intra-arterial digital subtraction angiographic series, except that they are 3D volumes and not projection images. Similar to other contrast-enhanced MR angiographic methods, TRICKS improves delineation of carotid artery stenosis by minimizing saturation effects. TRICKS and other contrast-enhanced MR angiographic techniques use short echo times and small voxels, thus reducing intravoxel dephasing. Surface morphology of atherosclerotic plaque and slow flow in nearly occluded vessels ("string sign") are well delineated. The major advantage of the TRICKS technique is that the timing of the acquisition in relation to the passage of the contrast bolus occurs automatically, allowing for consistent capture of the arterial phase. and eliminating the need for sophisticated synchronization methods.

Carotid Arteries↗

PubMed2001

Carotid bifurcation: evaluation of time-resolved three-dimensional contrast-enhanced MR angiography.

A magnetic resonance (MR) angiographic protocol was evaluated in the carotid bifurcation with use of a pulse sequence for time-resolved three-dimensional imaging of contrast material kinetics. The enhancement ratio, a quantitative measure of contrast enhancement, indicated that all studies included an image obtained near the peak of the intraarterial concentration of contrast agent (enhancement ratio, 90% +/- 9 [standard deviation]). Studies acquired at a higher frame rate (4.1-4.9 seconds) exhibited less venous enhancement (enhancement ratio, 25% +/- 16) than studies acquired with slower (6.0-9.6-second) frame rates (enhancement ratio, 46% +/- 25).

Adult↗

PubMed2001

Frequencies contributing to functional connectivity in the cerebral cortex in "resting-state" data.

BACKGROUND AND PURPOSE: In subjects performing no specific cognitive task ("resting state"), time courses of voxels within functionally connected regions of the brain have high cross-correlation coefficients ("functional connectivity"). The purpose of this study was to measure the contributions of low frequencies and physiological noise to cross-correlation maps. METHODS: In four healthy volunteers, task-activation functional MR imaging and resting-state data were acquired. We obtained four contiguous slice locations in the "resting state" with a high sampling rate. Regions of interest consisting of four contiguous voxels were selected. The correlation coefficient for the averaged time course and every other voxel in the four slices was calculated and separated into its component frequency contributions. We calculated the relative amounts of the spectrum that were in the low-frequency (0 to 0.1 Hz), the respiratory-frequency (0.1 to 0.5 Hz), and cardiac-frequency range (0.6 to 1.2 Hz). RESULTS: For each volunteer, resting-state maps that resembled task-activation maps were obtained. For the auditory and visual cortices, the correlation coefficient depended almost exclusively on low frequencies (<0.1 Hz). For all cortical regions studied, low-frequency fluctuations contributed more than 90% of the correlation coefficient. Physiological (respiratory and cardiac) noise sources contributed less than 10% to any functional connectivity MR imaging map. In blood vessels and cerebrospinal fluid, physiological noise contributed more to the correlation coefficient. CONCLUSION: Functional connectivity in the auditory, visual, and sensorimotor cortices is characterized predominantly by frequencies slower than those in the cardiac and respiratory cycles. In functionally connected regions, these low frequencies are characterized by a high degree of temporal coherence.

Adult↗

PubMed2000

Six-month test-retest reliability of MRI-defined PET measures of regional cerebral glucose metabolic rate in selected subcortical structures.

Test-retest reliability of resting regional cerebral metabolic rate of glucose (rCMR) was examined in selected subcortical structures: the amygdala, hippocampus, thalamus, and anterior caudate nucleus. Findings from previous studies examining reliability of rCMR suggest that rCMR in small subcortical structures may be more variable than in larger cortical regions. We chose to study these subcortical regions because of their particular interest to our laboratory in its investigations of the neurocircuitry of emotion and depression. Twelve normal subjects (seven female, mean age = 32.42 years, range 21-48 years) underwent two FDG-PET scans separated by approximately 6 months (mean = 25 weeks, range 17-35 weeks). A region-of-interest approach with PET-MRI coregistration was used for analysis of rCMR reliability. Good test-retest reliability was found in the left amygdala, right and left hippocampus, right and left thalamus, and right and left anterior caudate nucleus. However, rCMR in the right amygdala did not show good test-retest reliability. The implications of these data and their import for studies that include a repeat-test design are considered.

Adult↗

PubMed2000

Compensation of susceptibility-induced signal loss in echo-planar imaging for functional applications.

Functional magnetic resonance imaging favors the use of multi-slice gradient-recalled echo-planar imaging due to its short image acquisition times, whole brain coverage and sensitivity to BOLD contrast. However, despite its advantages, gradient-recalled echo-planar imaging also is sensitive to static magnetic field gradients arising primarily from air-tissue interfaces. This can lead to image artifacts such as voxel shifts and complete signal loss. A method to recover signal loss by adjusting the refocusing gradient amplitude in the slice-select direction, preferably axially, is proposed. This method is implemented as an automated computer algorithm that partitions echo-planar images into regions of recoverable signal intensities using a histogram analysis and determines each region's proper refocusing gradient amplitude. As an example, different refocusing gradient amplitudes are interleaved in a fMRI acquisition to maximize the signal to noise ratio and obtain functional activation in normal and dropout regions. The effectiveness of this method is demonstrated by recovering signal voids in the orbitofrontal cortex, parahippocampal/amygdala region, and inferior visual association cortex near the cerebellum.

Algorithms↗

PubMed2000

Mapping functionally related regions of brain with functional connectivity MR imaging.

BACKGROUND AND PURPOSE: In subjects who are performing no prescribed cognitive task, functional connectivity mapped with MR imaging (fcMRI) shows regions with synchronous fluctuations of cerebral blood flow. When specific tasks are performed, functional MR imaging (fMRI) can map locations in which regional cerebral blood flow increases synchronously with the performance of the task. We tested the hypothesis that fcMRI maps, based on the synchrony of low-frequency blood flow fluctuations, identify brain regions that show activation on fMRI maps of sensorimotor, visual, language, and auditory tasks. METHODS: In four volunteers, task-activation fMRI and functional connectivity (resting-state) fcMRI data were acquired. A small region of interest (in an area that showed maximal task activation) was chosen, and the correlation coefficient of the corresponding resting-state signal with the signal of all other voxels in the resting data set was calculated. The correlation coefficient was decomposed into frequency components and its distribution determined for each fcMRI map. The fcMRI maps were compared with the fMRI maps. RESULTS: For each task, fcMRI maps based on one to four seed voxel(s) produced clusters of voxels in regions of eloquent cortex. For each fMRI map a closely corresponding fcMRI map was obtained. The frequencies that predominated in the cross-correlation coefficients for the functionally related regions were below 0.1 Hz. CONCLUSION: Functionally related brain regions can be identified by means of their synchronous slow fluctuations in signal intensity. Such blood flow synchrony can be detected in sensorimotor areas, expressive and receptive language regions, and the visual cortex by fcMRI. Regions identified by the slow synchronous fluctuations are similar to those activated by motor, language, or visual tasks.

Adult↗

PubMed1999

Contrast-enhanced MR angiography of the carotid bifurcation.

With contrast-enhanced MR angiographic techniques, a T1-shortening contrast agent is injected into the blood stream. Imaging during the first pass of the contrast agent permits acquisition of a high-contrast MR angiogram. Scan parameters such as flip angle, repetition time, echo time, and scan duration, and injection parameters, such as dose and rate, must be carefully chosen to achieve maximum contrast between blood vessels and stationary tissues. A critical parameter affecting image quality is the timing of the acquisition relative to the injection. If the collection of the center of k-space does not coincide with peak arterial concentration, artifacts, reduced SNR, and venous enhancement may result. Several techniques have been developed to address the timing issue. Post-processing techniques such as subtracting a pre-contrast image from a post-contrast angiogram can be used to improve image quality. Intravascular contrast agents that may also lead to improved image quality are currently being developed.

Angiography, Digital Subtraction↗

PubMed1999

A post-processing technique for displaying vessels from routine fast-spin-echo images: MRI-derived angiography.

Fast-spin-echo magnetic resonance (MR) images are routine components of a standard MR brain examination. On these images, blood vessels are visible as black flow void. We report that by applying an enhancement filter to a stack of routine fast-spin-echo MR images, projected angiographic images can be generated. The vascular detail in the projected image is similar to that observed in a phase-contrast image. In addition to its advantage in obtaining vessel information from routine images, the proposed post-processing technique is fast, easy to implement and completely automatic. These images provide additional vessel information that is useful when MR angiography is unavailable or as an aid in planning dedicated MR angiographic studies.

Brain↗

PubMed1999

The clinical applications of functional MR imaging.

Functional MR imaging, similar to positron-emission tomography, shows the regions in which cerebral blood flow changes as neurons are active in the performance of cognitive tasks. Blood flow increases (activation) exceed that needed to supply oxygen for the increased metabolic needs for the increased neuronal activity. Therefore, in regions with activation, the deoxyhemoglobin concentration in the capillary blood decreases below levels found in the brain where neurons are not active.

Auditory Cortex↗

PubMed1999

The role of MR angiography in the evaluation of acute stroke.

Magnetic resonance angiography is an essential component of the acute stroke MR imaging work-up. Defining the location and extent of vascular compromise greatly aids in the selection of the appropriate therapy. In this article, the most common MR angiography manifestations of acute stroke are illustrated to emphasize the role of MR angiography in the evaluation of patients presenting with symptoms of acute cerebral ischemia.

Acute Disease↗

PubMed1998

Metabolic rate in the right amygdala predicts negative affect in depressed patients.

The role of the amygdala in major depression was investigated. Resting regional cerebral metabolic rate (rCMRglu) was measured with [18F]fluorodeoxyglucose positron emission tomography (PET) in two samples of subjects using two different PET cameras. The samples consisted of 10 and 17 medication-free depressives and 11 and 13 controls, respectively. Using coregistration of PET and magnetic resonance images, regions were individually delineated for the amygdala and thalamus, the latter of which was used as a control region. Within the depressed groups, right amygdalar rCMRglu was positively correlated with negative affect. Thalamic rCMRglu was not related to negative affect, and amygdalar rCMRglu accounted for a significant portion of variance in depressives' negative affect scores over and above the contribution of thalamic rCMRglu.

Amygdala↗

PubMed1998

Reproducibility of fMRI results across four institutions using a spatial working memory task.

Four U.S. sites formed a consortium to conduct a multisite study of fMRI methods. The primary purpose of this consortium was to examine the reliability and reproducibility of fMRI results. FMRI data were collected on healthy adults during performance of a spatial working memory task at four different institutions. Two sets of data from each institution were made available. First, data from two subjects were made available from each site and were processed and analyzed as a pooled data set. Second, statistical maps from five to eight subjects per site were made available. These images were aligned in stereotactic space and common regions of activation were examined to address the reproducibility of fMRI results when both image acquisition and analysis vary as a function of site. Our grouped and individual data analyses showed reliable patterns of activation in dorsolateral prefrontal cortex and posterior parietal cortex during performance of the working memory task across all four sites. This multisite study, the first of its kind using fMRI data, demonstrates highly consistent findings across sites.

Adult↗

PubMed1998

Contrast-enhanced 3D MR DSA of the carotid artery bifurcation: preliminary study of comparison with unenhanced 2D and 3D time-of-flight MR angiography.

PURPOSE: To compare the delineation of stenosis at the carotid artery bifurcation on three-dimensional (3D) magnetic resonance (MR) digital subtraction angiographic (DSA) images with that on two-dimensional (2D) and 3D time-of-flight (TOF) MR angiographic images. MATERIALS AND METHODS: Twenty-six patients with 29 carotid artery bifurcations and symptoms of cerebral ischemia underwent 3D MR DSA. A time-resolved series was generated with 3D MR DSA after the bolus injection of gadodiamide. The resolution for a carotid artery examination was 0.4 x 0.4 x 1.0 mm, with volumes reconstructed at 4.5-second intervals. The 3D MR DSA images were compared with contemporaneously acquired unenhanced 2D and 3D TOF images. Two observers ranked the 2D and 3D TOF MR angiographic and 3D MR DSA images according to the following: (a) stenosis delineation, (b) internal carotid artery delineation, (c) intravascular signal intensity, and (d) diagnostic confidence. RESULTS: The mean ranking for diagnostic confidence was 1.10 (1 = best technique, 3 = worst technique) for 3D MR DSA. Compared with the pooled 2D TOF and 3D TOF ranks, the 3D MR DSA rank was significantly better (P < .01). Similar levels of statistical significance were found for the other criteria. CONCLUSION: Three-dimensional MR DSA improves the delineation of carotid arterial stenosis by virtually eliminating saturation effects and reducing intravoxel dephasing. Surface morphology and nearly occluded vessels ("string sign") were easily identified. Confidence in identifying carotid arterial occlusions was also very high with this technique.

Angiography, Digital Subtraction↗

PubMed1998

Treatment of high-grade spinal cord astrocytoma of childhood with "8-in-1" chemotherapy and radiotherapy: a pilot study of CCG-945. Children's Cancer Group.

OBJECT: The purpose of this study was to devise an improved method of treating high-grade gliomas of the spinal cord in children who have a dismal prognosis following conventional treatment. METHODS: Eighteen children with newly diagnosed high-grade astrocytomas arising in the spinal cord were enrolled in the Children's Cancer Group (CCG) protocol 945. Following surgery, they were all assigned to receive two cycles of "8-drugs-in-1-day" (8-in-1) chemotherapy prior to radiotherapy and eight additional cycles thereafter. A centralized neuropathology review was used to confirm the diagnosis of high-grade astrocytoma in 13 of the 18 children: anaplastic astrocytoma (eight patients), glioblastoma multiforme (four patients), and mixed malignant glioma (one patient). Diagnoses were discordant in five patients. There were eight boys and five girls in the group with confirmed diagnoses, with a median age of 7 years (range 1-15 years). The extent of resection was confirmed by computerized tomography or magnetic resonance (MR) evaluation in five of 13 patients. There were six gross-total or near-total resections (> 90%), four partial or subtotal resections (10-90%), and three biopsies. Six patients showed evidence of leptomeningeal metastases at diagnosis based on staging MR examinations. Eight of the 13 patients completed at least eight of the prescribed 10 cycles of chemotherapy; five received craniospinal radiotherapy and five spinal radiotherapy. CONCLUSIONS: The 5-year progression-free and total survival rates for the 13 children were 46 +/- 14% and 54 +/- 14%, respectively. Seven patients suffered a relapse at the primary site, four of whom also had leptomeningeal metastases. Seven of the 13 patients (54%) remain alive at the time of this report at a median of 76 months (range 51-93 months) from study entry. Six patients died between 8 and 38 months after diagnosis, all with active disease. Intensification of therapy may further improve outcome in this high-risk population.

Adolescent↗

PubMed1998

Current neurosurgical management and the impact of the extent of resection in the treatment of malignant gliomas of childhood: a report of the Children's Cancer Group trial no. CCG-945.

OBJECT: One hundred seventy-two children with high-grade astrocytomas were treated by members of the Children's Cancer Group in a prospective randomized trial designed to evaluate the role of two chemotherapy regimens. Seventy-six percent of the patients (131 children) in whom a diagnosis of either anaplastic astrocytoma or glioblastoma multiforme was confirmed by central pathological review are the subject of this report. METHODS: Patients were stratified according to the extent of tumor resection (biopsy [< 10%], partial resection [10-50%], subtotal resection [51-90%], near-total resection [> 90%], and total resection) as determined by surgical observation and postoperative computerized tomography scanning. Information on contemporary neurosurgical management was obtained from the patient's operative records and standardized neurosurgical report forms. The vast majority of tumors were supratentorial: 63% (83 tumors) in the superficial cerebral hemisphere, 28% (37 tumors) in the deep or midline cerebrum, and only 8% (11 tumors) in the posterior fossa. A significant association was detected between the primary tumor site and the extent of resection (p < 0.0001). A radical resection (> 90%) was performed in 37% of the children: 49% of the tumors in the superficial hemisphere and 45% of tumors in the posterior fossa compared with 8% of midline tumors. Tumor location could also be used to predict the need for both temporary and permanent cerebrospinal fluid (CSF) diversion. Half of the deep tumors and 8% of the hemispheric astrocytomas ultimately required a permanent CSF shunt. Improvement in preoperative neurological deficits and level of consciousness was seen in 36% and 34% of the children, respectively. New or increased deficits were present in 14% of the children, with 6% experiencing a diminished sensorium after surgery. Postoperative nonneurological complications were rare: infection, hematoma, and CSF fistula each occurred in 1.7% of the children. Univariate and multivariate analyses demonstrated that radical tumor resection (> 90%) was the only therapeutic variable that significantly improved progression-free survival (PFS) rates. For all patients with malignant astrocytomas, the distributions of PFS rates were significantly different (p = 0.006) following radical resection compared with less extensive (< or = 90%) resection. The 5-year PFS rates were 35 +/- 7% and 17 +/- 4%, respectively. The differences in the distribution of PFS rate were significant for the subsets of patients with anaplastic astrocytoma (p = 0.055) and glioblastoma multiforme (p = 0.046). The 5-year PFS rates for anaplastic astrocytoma were 44 +/- 11% and 22 +/- 6% for cases in which the tumor was radically resected and less than radically resected, respectively; whereas the 5-year PFS rates for glioblastoma multiforme were 26 +/- 9% and 4 +/- 3% for cases in which the tumor was radically resected and less than radically resected, respectively. CONCLUSIONS: The demonstration of a survival advantage provided by radical resection should prompt neurosurgeons to treat malignant pediatric astrocytomas with aggressive surgical resection prior to initiation of radiotherapy or adjuvant chemotherapy.

Adolescent↗

PubMed1998

MR angiography of vascular malformations.

Magnetic resonance angiography (MRA) plays an important role in the evaluation of cerebrovascular disease. This is especially true in the diagnosis and management of cerebral vascular malformations. Both time-of-flight and phase contrast MRA techniques have proved useful for the imaging of all types of cerebral vascular malformations including AVMs, dural fistulas, cavernous malformations, and venous angiomas. The role of MRA in the evaluation of these lesions is discussed.

Brain↗